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2007 chevy trailblazer_ss_3ss
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208 Posts
Discussion Starter · #1 ·
This is a 2007 Trailblazer Super Sport equipped with the 395 HP 400 Ft LB engine.

When I take my foot off the accelerator and that powerful engine refuses to back off results in excessive braking force required. This condition is not predictable, but, is reproducible under the extreme conditions I show below.

Sudden stops on the freeway when this engine hang up occurs is the scariest. Running over a kid because of this keeps me awake at night.

GM doesn't care. I know. They paid me to go away when I showed this to them as a lemon. GM has seen my videos. There is still not a TSB or fix.

Several others also have this problem including a dealer demo GM took to the track. The "demo" had this problem so GM's attorney told me it was "normal". The lawsuit of mine and another fellow who did wreck has not gotten GM's attention. (Lawyers simply say they are not Nader.)

Time for page 553 in the manual: Reporting Safety Defect to the U.S. Gov't.

http://www-odi.nhtsa.dot.gov/ivoq/index.cfm

Join me in filling one of these forms out if your TBSS has these symptoms with the link above. It may save someone's life. Like yours or your loved ones. GM isn't going to do anything without "encouragement".

Here is some of the history and others who have this issue. Even though I can lesson this effect up with a tune, the hotter it gets outside the worse I have this problem, including some symptoms even with a tune. Stock tune my TBSS is plain unsafe to drive as the video repost section below shows.

History:
http://forums.trailvoy.com/showthread.php?t=40717

Video Repost below:

If I let off the brakes when the engine speed hangs up my TBSS will accelerate on it's own.

Video 1 (5MB) is the acceleration letting off the brakes. ~500 RPM increase with no throttle.
http://members.cox.net/ttllc/tbss/1.mpg

Video 2 (5MB) is the attempted acceleration with the brakes on to a full stop and the violent throttle reduction when speed = 0 MPH. The Computer is literally power braking when coming to a stop and suddenly kills power - the lurch you see in the video.
http://members.cox.net/ttllc/tbss/2.mpg

After logging the ECM is simply not closing the throttle. I am down to a sensor being out of calibration or a defective in design program/factory tune. Reducing/changing the final idle airflow minimum vs RPM vs gear table in HPTuners helps 'cure' this problem. However, my TBSS doesn't do this all the time. I feel because of that there is a performance or abuse mode that either adds to this table to prevents the throttle from closing.

If you get on it, doesn't have to be WOT, and then try and stop you are likely to run into this hangup. Over 70 degrees and AC clutch running, not just AC on, while trying to stop is the worst case. AC does not have to be on for the hang to happen. Happens in all gears including 4th at freeway speed. Slightly worse in manual 3rd etc.

The Throttle pedal is logged at 0% during the acceleration. It is not sticking and my foot is off it.
 

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2006 chevy
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215 Posts
... I'm no mechanic ...but based on both videos it looks like an automatic tranny doing a downshift (with rev matching) to me...

You ran up 1st gear, the beast shifted to 2nd when you left off, then lifted the RPM's slightly to get back into 1st when RPM's dropped too low. If the speed of the vehicle didn't actually increase, which wasn't shown in the speedo, I don't think you have a problem.

You may feel that you need to brake more once it shifts to first, I think that's just because first has more torque than 2nd at low RPM's.
 
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